This paper treats the relationship between natural law and Cicero's code of laws, as presented in Cicero's work On Laws . In response to recent interpretations, it argues that Cicero's code is not identical with natural law. Instead, his laws participate imperfectly in the commands and prohibitions of natural law. Just as Cicero uses a Stoic conception of natural law, so he uses a specifically Stoic view of participation in natural law. His laws share imperfectly in the guiding power of natural law by prescribing intermediate duties as a means to the attainment of virtue. Overall, Cicero's code of laws prefigures modern written constitutions in the attempt to found the basic laws of a state on an unchanging moral norm.